Is there a relationship between loss of smell and Alzheimer's?

New study finds people with biological indicators of Alzheimer's disease have trouble distinguishing various smells.

Scientists have been making progress on possible ways to detect early signs of Alzheimer’s before the disease takes total control.
(Photo: Halfpoint/Shutterstock)

Detecting early signs of Alzheimer’s disease isn’t an easy
task. By the time an individual experiences symptoms and is diagnosed with
Alzheimer’s, it’s often too late. At the point of diagnosis, a person’s memory
has reached the point of decline, and that’s pretty much the indicator that
Alzheimer’s has set in. Although the progression is difficult to detect — and the
rate of progression varies among individuals — it’s believed that changes in brain function due to
Alzheimer’s can begin
almost 20 years before clear evidence appears.

Luckily, in recent years scientists have been making
progress on possible ways to detect early signs of Alzheimer’s before the
disease takes control.

Sensing some initial
correlations

In 2013, researchers from the University of Florida conducted
a
study that used peanut butter to look at correlations between difficulties with odor detection and
Alzheimer’s. The researchers found that participants with mild cognitive
impairment, Alzheimer’s and various forms of dementia had a tougher time
identifying the peanut butter odor when using their left nostril as opposed to
the right nostril. Now, more recent research has given us more concrete
evidence that examining early olfactory loss could be an effective way to track
the onset of the disease.

A focus on olfactory
distinction

Study participants with stronger biological indicators of Alzheimer’s had a more difficult time making the distinction between various scents. (Photo: Syda Productions/Shutterstock)

The new study was
conducted by scientists at McGill University and was published in the
journal Neurology in July 2017. For this study, the researchers focused on a participant’s ability to make a distinction between a number of different scents during scratch-and-sniff tests. Participants were asked to distinguish and identify various scents such as gasoline, bubble gum and lemon, reports Science Daily.

Roughly 300 participants took part in the study. The average age was 63, and these individuals were at a
higher risk of developing the disease because they had a parent who experienced
Alzheimer’s. One hundred of the participants also volunteered to undergo regular lumbar
punctures (spinal taps) to measure quantities of various Alzheimer’s-related proteins that can be found in
cerebrospinal fluid.
Cerebrospinal fluid is a body fluid that is present in the brain and spinal cord
that allows the brain to rid itself of waste products and protect the brain
from injury, along with other various functions.

It turns out that
participants with stronger and purely biological indicators of Alzheimer’s had a
more difficult time making the distinctions between the various scents.

“This is the first time that anyone has been able to show
clearly that the loss of the ability to identify smells is correlated with
biological markers indicating the advance of the disease,” says Marie-Elyse
Lafaille-Magnan, a McGill doctoral student and the study’s first author. “For more than 30 years, scientists have been exploring the connection
between memory loss and the difficulty that patients may have in identifying
different odors. This
makes sense because it’s known that the olfactory bulb (involved with the sense
of smell) and the entorhinal cortex (involved with the memory and naming of
odors) are among the first brain structures first to be affected by the
disease.”

The future of
tracking the progression of Alzheimer's

While the current research doesn’t offer much insight in
terms of a cure, it allows scientists to better track the
progression and mitigate the effects of Alzheimer’s.

"Despite all the research in the area, no
effective treatment has yet been found for AD," says Dr. John Breitner, an
author of the study and the director of the Center for Studies on Prevention of
Alzheimer's Disease at the Douglas Mental Health Research Center of McGill
University. “But, if we can delay the onset of symptoms by just five years, we
should be able to reduce the prevalence and severity of these symptoms by more
than 50 percent."

Not only does the new research allow for a better
tracking method, but it also gives us a method that's less costly.

"This means that a simple smell test may
potentially be able to give us information about the progression of the disease
that is similar to the much more invasive and expensive tests of the
cerebrospinal fluid that are currently being used," says Dr. Judes
Poirier, the director of research program on Aging, Cognition and Alzheimer's
disease of the Douglas Institute and fellow study author.

But even
though this research is a step in the right direction, we shouldn’t accept the
new smell test method as the end-all be-all method for tracking Alzheimer’s.
Poirier adds, “problems identifying smells may be indicative of other medical
conditions apart from AD and so should not be substituted for the current
tests."

While tracking the progression of Alzheimer’s is tricky business, we now have a better sense for methods of early
detection.